Transcription and Translation

The Three Types of Experiments

Still in Italy. Here’s another old entry for you.

I’m not sure about the history of “the three types of experiments” (3 T’s), but they are referred to quite often in the labs I’ve been in. So what exactly are they?

Here goes …

Type A Experiment: every possible result is informative.
Type B Experiment: some possible results are informative, other results are uninformative.
Type C Experiment: every possible result is uninformative.

There is even a little saying that accompanies this …

The goal is to maximize type A and minimize type C.

There are some that even name the 3tes 1 through 3 instead of A, B and C. I have a few comments about the whole “three types of experiments” (hey that’s what blogs are for!)

First, the 3tes are very helpful for younger inexperienced scientists. When ever you perform an experiment, ask yourself “what will I learn from this” or better “what will I learn from each potential result”. This not only helps to avoid performing nonsensical (i.e. type C) experiments, but helps to think about setting the proper control experiments. These controls often turn experiments of the type C variety into the type A/B variety.

Second, about that saying I quoted above … I have a problem with it. The saying implies that type A experiments are the most important ones, when realy it’s type B experiments that give you the most insight.

What do I mean by that?

One main activity of scientists, is to figure out how things work. At the beginning of a project we mull over observations that we have made, we read the literature to see what others have said, and then we come up with a hypothesis. “This is how may it work” we exclaim.

Our hypothesis may be ingenious or pedestrian, but there are probably hundreds of valid hypothesis that one could conceive. Well then what? … start an institute and hire a PR firm?

No. The best approach is to figure out the implications of your hypothesis, and then to see if this corresponds to reality. (That’s science!) These implications are called “testable predictions”. These are type B experiments. If the prediction holds, the hypothesis is good (for now), if the prediction doesn’t hold our poor scientist must go back to the drawing board. In the end, science advances by this line of research. Type A experiments always suppose that your hypothesis is essentially correct and help address details such as “does it work this way or that way”, “fast or slow”, “does it require energy in the form of ATP” … important questions, but as Kuhn would say, in the end they are filling in the holes.

So that’s all I have to say about the 3tes, but if anyone knows “the history”, please let me know.


  1. #1 SMC
    September 26, 2007

    Or in other words, the “Type A(1)” experiments are for examining how things work, whereas “Type B(2)” experiments are concerned with the more fundamental question of why things work.

  2. #2 micromagnets
    September 26, 2007

    I always think of type B as those where the negative answer may be due to artifacts or a poorly designed experiment. Type A can also give you a “no” answer and if your controls are good then this is informative.

  3. #3 sean john
    September 27, 2007

    Its clear that science is drugery and hasn’t saved us a bit from ourselves or our work. We set up the experiement to find a certain result. Often inventions are by accident or Godhead serendipity. I’m doing this comment as an experiment to see how lucky I am at winning contests.
    I am also using ESP right now. I expect that this comment with Heisenberg uncertainty with certainty.

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